1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for a debris barrier assembly for downhole tools.
2. Description of the Related Art
Wells are typically formed using two or more strings of casing. Generally, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps with the lower portion of the upper string of casing. The second “liner” string is then fixed or “hung” off of the upper surface casing. Afterwards, the liner is also cemented. This process is typically repeated with additional liner strings until the well has been drilled to total depth.
The process of fixing a liner to a string of surface casing or other upper casing string involves the use of a liner hanger and a packer assembly. The liner hanger is typically run into the wellbore above the liner string itself. The liner hanger is actuated once the liner is positioned at the appropriate depth within the wellbore. The liner hanger is typically set through actuation of slips which ride outwardly on cones in order to frictionally engage the surrounding string of casing. The liner hanger operates to suspend the liner from the casing string. The packer assembly is connected above the liner hanger and may be actuated to provide a seal between the liner and the casing. A polished bore receptacle (“PBR”) is connected above the packer assembly to facilitate setting of the packer.
The assembly of liner, liner hanger, and packer assembly are typically run into the well using a running assembly having a running tool, a setting assembly, and a debris barrier. One type of debris barrier is known as a junk bonnet. The running assembly is inserted into the PBR and the liner. The running tool is actuated to releasably retain the liner assembly. The setting assembly is positioned above the running tool and includes a plurality of spring-loaded dogs. The debris barrier is connected above the setting assembly and proximate an upper portion of the PBR. The debris barrier is intended to prevent debris from entering the PBR, such as during the cementing process. After actuating the liner hanger, the packer is set by lifting the setting assembly above the PBR to allow the spring loaded dogs to spring radially outward. Thereafter, the dogs are urged against the top end of the PBR to apply an axial force downward to set the packer.
While lifting the setting assembly out of the PBR, the top end of the debris barrier is also lifted out of the PBR. Without the debris barrier plugging the PBR, the top end of the PBR is opened to the wellbore. Debris is thus allowed to enter the PBR. The debris may disrupt the performance of the operation by entering the tool assemblies or fluid passages.
There is a need, therefore, for a debris barrier adapted to prevent debris to enter the PBR or other tools during the liner installation process.